Splenectomy remains a treatment in patients with autoimmune thrombocytopenic purpura (ATP) who fail to respond adequately to conservative treatment. We report on a 78-year-old man who developed ATP after splenectomy performed six years earlier for iatrogenic injury to the spleen during hemicolectomy. Incidentally, he suffered from colonic and prostatic malignancies. To our knowledge, such a case has not been reported before. We discuss the mechanism of thrombocytopenia in ATP and its association with various malignancies.